Conventionally, touch panels of various schemes have been proposed or introduced commercially as apparatuses which input coordinates by pointing on an input surface with a pointer or a finger. The touch panels are widely used because a PC or the like can easily be operated on the screen without using any special tool.
There are various schemes using, e.g., a resistive film or an ultrasonic wave. An apparatus using light is also disclosed (e.g., U.S. Pat. No. 4,507,557). In this apparatus, a retroreflecting sheet is arranged outside the coordinate input surface. Light from a means for illuminating the input surface with light is reflected by the retroreflecting sheet, and a light amount distribution is detected by a light-receiving means. In this arrangement, the angle of a region shielded by a finger or the like in the input region is detected, thereby determining the coordinates of the shielded position, i.e., the input position.
Such a coordinate input apparatus is mounted on the surface of a rear projector or plasma display panel, and a PC window is displayed. Then, a large interactive display capable of operating a PC by a finger or a pointer or inputting the locus of handwriting can be formed.
In such an interactive arrangement, pointing on an icon or the like can easily be done by using a finger or a pointer. However, since the retroreflecting member has a height to some degree, there is an input height to some degree from the screen. When, e.g., a finger is used for input., the finger is detected before it reaches the screen. This poses no so serious problem if a position is simply designated by pointing. However, in inputting characters, dots or lines are connected together, and input is difficult.
As a countermeasure, for example, a plurality of threshold values are set, and the input depth is detected. Only cursor movement is done until the input depth has a predetermined value or more. If it is determined that the input depth has a predetermined value or more, the state is determined as pen-down. In this case, a line is drawn on the screen, or an icon is selected as if the left button of a mouse were clicked on, thereby reducing connection of lines and dots (e.g., Japanese Patent Laid-Open No. 2001-84106).
In this method, however, it is difficult to detect the pen-down state only when proper contact with the screen is obtained. That is, there may be a little difference from human sensation.
An apparatus is disclosed in which to reliably detect contact with the screen, a pointer is used, and a pen-down state is detected in accordance with its contact (e.g., Japanese Patent Laid-Open No. 2002-49466). In this method, the position pointing means on the pen uses a movable point. The light reflection characteristic is changed by moving the pen point, thereby obtaining pen-down information.
When this method is used, the pen-down state can be detected in accordance with contact with the screen. However, since the state is represented mechanically, it is difficult to send to the main body other pieces of information of the pointer, including, e.g., information corresponding to the right button of a mouse and information that represents the ID of a pen to cope with such an application that changes the pen color.
Other information may be sent by using an electromagnetic wave, infrared radiation, or ultrasonic wave. However, when a switch signal is transmitted by using an ultrasonic wave, reflection from objects around the device may occur in some device installation state so the reliability may be low. When an ultrasonic wave or electromagnetic wave is used, and devices are placed side by side, interference between adjacent devices may occur.
A method using infrared radiation can suitably be used for transmission/reception of various kinds of information such as pen-down information, side switch information, and ID information. In this method, even when reflection occurs, no problem is posed because the speed of infrared radiation is high. Even when devices are installed side by side, they can be shielded from each other by a very simple structure.
The above-described coordinate input apparatuses using retroreflection rarely use visible light that can disturb display. They also often use infrared light for coordinate detection. In this case, the light-receiving means in the imaging optical system for coordinate detection and the light-receiving means in the condensing optical system that receives the information of the pointer detect each other's light. For example, assume that during detection of reflected light from the retroreflecting member, the pointer emits light to transmit information near the light-receiving means in the imaging optical system for coordinate detection. At this time, the detection unit in the imaging optical system may detect the light, and a coordinate detection error may occur. Alternatively, if light from the pointer is strong, the light-receiving element in the imaging system may be saturated, and detection may become impossible.
Even when the condensing optical system which detects the optical signal from the pointer is designed not to directly face the light source for coordinate detection, light for coordinate detection may be reflected by a finger or the pointer near the light-receiving element in the condensing optical system and detected. In this case, no correct information can be obtained from the pointer.